1. Field of the Invention
The present invention relates to an internal combustion engine with a cam phase change mechanism capable of changing the phase of an intake cam.
2. Description of the Related Art
Conventionally, there are internal combustion engines that comprise a cam phase change mechanism as a variable valve gear, which changes the phase of an intake cam to vary the opening and closing timings of an intake valve. Further, a technique has been developed in which the cam phase change mechanism is applied to internal combustion engines that are provided with a plurality of intake valves for each cylinder. According to this technique, the opening and closing timings of only some of the intake valves are varied in accordance with the load and engine speed.
In one such internal combustion engine, the opening and closing timings of some of the intake valves are delayed in, for example, a high-speed, high-load mode, whereby the open period of the intake valves, including those which are not subjected to delay-angle control, is extended to increase the flow rate of intake air for the security of output. In order to secure an appropriate compression ratio, as in a low-speed, high-load start mode, on the other hand, the delay angle of the intake valves is limited (Jpn. Pat. Appln. KOKAI Publication No. 3-202602).
Since the delay angle of the intake valves are limited in the start mode, according to the technique described in the above patent document, however, the intake valves share the same open period, so that flows of intake air interfere with one another, thereby suppressing generation of swirls, in a combustion chamber. Thus, combustibility may be reduced, possibly resulting in a reduction in exhaust performance.